RNASE-III DEFICIENT SALMONELLA-TYPHIMURIUM LT2 CONTAINS INTERVENING SEQUENCES (IVSS) IN ITS 23S RIBOSOMAL-RNA

Salmonella typhimurium LT2 contains intervening sequences (IVSs) of 90 -110 nt within all its 23S rRNA that are cleaved out by RNase III, res ulting in rRNA fragmentation. In order to determine the functionality of 23S rRNA that contains unexcised IVSs, we constructed an S. typhimu rium RNase III (rnc) deficient strain by transducing a mini-Tn10 (rnc- 14::Tn10) from Escherichia coli K-12. The resulting strain of S. typhi murium was viable, contained IVSs within all of its 23S rRNA, and show ed a growth reduction similar to that observed for the RNase III defic ient strain of E. coli. These results indicate that ribosomes containi ng 23S rRNA in which IVSs are not excised are functional in translatio n, and make it unlikely that RNase III excision of IVSs from strain LT 2 23S rRNA is dictated by a selective pressure to uphold the functiona l integrity of ribosomes. (C) 1998 Federation of European Microbiologi cal Societies. Published by Elsevier Science B.V.